1. Field of the Invention
The present invention relates to methods of making electronic devices and the electronic devices themselves. The invention additionally relates to electronic devices obtainable by the methods of the invention. The devices and methods of the present invention are particularly advantageous, since electrical leakage from the cathode on top of the device stack to the hole injection layer is minimised or eliminated.
2. Related Technology
Methods for manufacturing electronic devices involving the deposition of active components from solution (solution processing) have been extensively investigated. If active components are deposited from solution, one problem is how to contain the active components in desired areas of the substrate. One solution to this problem is to provide a substrate comprising a patterned bank layer defining wells in which the active components can be deposited from solution. The wells contain the solution while it is drying, such that the active components remain in the areas of the substrate defined by the wells.
These methods have been found to be particularly useful for deposition of organic materials from solution. The organic materials may be conductive, semi-conductive, and/or opto-electronically active, such that they can emit light when an electric current is passed through them or detect light by generating a current when light impinges upon them. Devices which utilize these materials are known as organic electronic devices. An example is an organic transistor device. If the organic material is a light-emissive material, the device is known as an organic light-emissive device (OLED).
Thin film transistors (TFTs), and in particular organic thin film transistors (OTFTs) may be manufactured by low cost, low temperature methods such as solution processing. In these devices, it is particularly important to contain the organic semiconductor (OSC) within the right areas and channels of the device. It is known to provide a bank which defines wells in order to contain the OSC. However, even when using such a well-defining bank, wetting of the bank layer may occur if the contact angle of the OSC solution on the bank is too low. It is also known to control the wettability of the bank by coating with a fluorine based plasma. Other methods include using material with inherently low wettability.
Some devices may require more than a single OSC layer. A typical organic light emitting device (OLED), such as one used in a display, may have two layers of organic semiconductor material—one may be a layer of light emitting material, such as a light-emitting polymer (LEP), and the other may be a layer of a hole transporting material, such as a polythiophene derivative or a polyaniline derivative. In certain circumstances it is an advantage to form a double bank structure such that the first and second bank layers define a step structure around the wells formed by the banks. Such a structure can allow the wells to be overfilled with solution. Such dual bank systems exist with 2 layers, or steps, but the lower/inner bank has typically not been included as a separate pinning/filling point for the first layer of organic semiconductor material. In other systems the lower/inner bank may act as a mask (to mask off edge emission effects), or as a means to improve fluid wetting around the edge of the filled area, but the whole area (up to the upper/outer bank edge) is filled (or intended to be filled) by all organic semiconductor layers, and they share the same pinning point.
WO 2009/077738 discloses a double bank structure providing two different pinning points for different fluids deposited in the wells, one at the edge of the first layer around the well and one at an edge of the second layer stepped back from the well. This can ensure, for example, that on drying a second material deposited in the wells completely covers a first material, particularly around the edges of the wells.